Objects and materials having a hard coating thereon find wide application. However, the full utilization of hard coatings has been limited by mismatches of, e.g., coefficient of thermal expansion, modulus of elasticity, lattice parameter, extent of crystallinity, degree of crystallinity, and compositional and/or structural dissimilarity, between the substrate and the coating.
For example, while plastic optical elements and transparencies are subject to abrasion and hazing, plastic articles having hard coatings thereon find utility in many areas.
For example, hard coatings applied to the outside surfaces of optical fibers provide protection to plastic optical fibers. This eliminates the need for cladding.
Other applications of hard coated plastic optical elements are in mirrors for high energy lasers.
Plastic is also used as the refractive element in lenses, for example ophthalmic lenses, and photographic, and telescopic lenses. Especially preferred are polycarbonate and polyallyl carbonate polymers for ophthalmic, sun glass, and safety goggle applications, and polymethyl methacrylate polymers for camera lenses, binocular lenses, telescope lenses, microscope objectives and the like. Plastic lenses have found good market acceptance and market penetration. However, the full potential of plastic lenses has been limited by their low resistance to abrasion; hazing, and scratching. Prior art abrasion resistant coatings, exemplified by polysilicate coatings and polysiloxane coatings, have not eliminated the problem of poor adhesion and poor abrasion resistance.
Plastic sheets with scratch and abrasion resistant coatings have found market acceptance in various automotive applications. These include headlight panels, sunroofs, side windows, and rear windows. However, the fuller utilization of plastic sheet material has been limited by the poor adhesion, and mismatch of thermal expansion coefficients between the plastic and the coating.
Large area plastic sheets have also found utility in applications such as doors, windows, walls, air craft windows, air craft canopies, vandalism and break-in resistant panels, windows and doors, and esthetic barriers. However, the poor abrasion resistance of these large sheets limit their more complete acceptance.
Plastic materials have also been utilized to provide a shatter resistant layer for large sheets of glass. The glass-plastic structure is exemplified by bi-layer windshields having a single sheet of glass on the weather incident side of the windshield, and a polymeric film, for example a polyurethane film, adherent to the glass on the interior side. These bi-layer windshields have not found market acceptance because of the very poor adhesion resistance to scratching and abrasion of the internal, polyurethane coating.
The inability to provide an adherent, abrasion resistant, substantially transparent coating has limited the full potential of the transparent plastics and other soft substrates.
Other materials which require a hard coating are semiconductors, e.g., photosensitive semiconductors. These semiconductors, utilized in, for example, imagers, photovoltaic cells, and electrophotographic drums, are subject to abrasion, scratching, and hazing. Photovoltaic cells are subject to these insults during manufacturing and service, while imagers and electrophotographic drums are subject to the scratching, scraping, and abrading effects of rough sliding documents. In the case of electrophotographic drums, these effects are exacerbated by submicron, particulate toners.